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| Titel |
Aged boreal biomass-burning aerosol size distributions from BORTAS 2011 |
| VerfasserIn |
K. M. Sakamoto, J. D. Allan, H. Coe, J. W. Taylor, T. J. Duck, J. R. Pierce |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 4 ; Nr. 15, no. 4 (2015-02-16), S.1633-1646 |
| Datensatznummer |
250119435
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| Publikation (Nr.) |
 copernicus.org/acp-15-1633-2015.pdf |
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| Zusammenfassung |
Biomass-burning aerosols contribute to aerosol radiative forcing on the
climate system. The magnitude of this effect is partially determined by
aerosol size distributions, which are functions of source fire
characteristics (e.g. fuel type, MCE) and in-plume microphysical processing.
The uncertainties in biomass-burning emission number–size distributions in
climate model inventories lead to uncertainties in the CCN (cloud condensation nuclei) concentrations
and forcing estimates derived from these models.
The BORTAS-B (Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellite) measurement campaign was designed to sample boreal
biomass-burning outflow over eastern Canada in the summer of 2011. Using
these BORTAS-B data, we implement plume criteria to isolate the
characteristic size distribution of aged biomass-burning emissions (aged
~ 1–2 days) from boreal wildfires in northwestern Ontario.
The composite median size distribution yields a single dominant accumulation
mode with Dpm = 230 nm (number-median diameter) and σ = 1.5, which are comparable to literature values of other aged plumes of a
similar type. The organic aerosol enhancement ratios (ΔOA / ΔCO) along the
path of Flight b622 show values of 0.09–0.17 μg m−3 ppbv−1 (parts per billion by volume) with no significant trend with distance from the source. This
lack of enhancement ratio increase/decrease with distance suggests no
detectable net OA (organic aerosol) production/evaporation within the aged plume over the
sampling period (plume age: 1–2 days), though it does not preclude OA
production/loss at earlier stages.
A Lagrangian microphysical model was used to determine an estimate of the
freshly emitted size distribution corresponding to the BORTAS-B aged
size distributions. The model was restricted to coagulation and dilution
processes based on the insignificant net OA production/evaporation derived
from the ΔOA / ΔCO enhancement ratios. We estimate that the
young-plume median diameter was in the range of 59–94 nm with modal widths
in the range of 1.7–2.8 (the ranges are due to uncertainty in the
entrainment rate). Thus, the size of the freshly emitted particles is
relatively unconstrained due to the uncertainties in the plume dilution
rates. |
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